首先搞清楚这句话，在 Ruby 中，方法分为
public、private
和 protected
三种，仅仅有 public
方法才干作为控制器的动作。

我的出错的代码例如以下：

controlle

class ArticlesController < ApplicationController
	def new
	end

	def create
		params.permit!
		@article = Article.new(params[:article])

		@article.save
		redirect_to @article
	end

	private
  		def article_params
    	params.required(:article).permit(:title, :text)
  	end

  	def show
  		@article = Article.find(params[:id])
  	end
end

view show.html.erb

<p>
	<strong>Title:</strong>
	<%= @article.title %>
</p>

<p>
	<strong>Text;</strong>
	<%= @article.text %>
</p>

报错说是：

NoMethodError in Articles#show

Showing /home/huihui/Documents/ruby/blog/app/views/articles/show.html.erb where line #3 raised:

undefined method `title‘ for nil:NilClass

解决方法是：

在controlle文件中：

class ArticlesController < ApplicationController
	def new
	end

	def create
		params.permit!
		@article = Article.new(params[:article])

		@article.save
		redirect_to @article
	end

  	def show
  		@article = Article.find(params[:id])
  	end

  	private
  		def article_params
    	params.required(:article).permit(:title, :text)
  	end
end

把show方法改成公有的就好啦

ruby on rails错误undefined method `title' for nil:NilClass